double tank equipment

[cool_hardware52]

Tobin,
How is that even possible? Assuming isolator is open when he/she blend it, or is it that even too much to assume?

It implies the Iso was shut, and that suggest competence issues with who ever filled the tanks.

Tobin

 

[eelnoraa]

oh, you beat me to it. I didn't read the previous sequence of post. I realized what was being discussed now. Thx,

 

[cool_hardware52]

Personally, I analyze on tank valve (or orifice or whatever the thing is called that you put the first stage on) if the regs are not installed. This is always the case when I pick up my tanks from the dive shop.

I analyze on a low pressure inflator hose if possible (backgas tanks) when I have regs installed.

In any case, I assume that the reading at the tank valve will be the same as the analysis on the second stage.




I wonder if anyone has any *actual* data or *real life* experience with this. The only way I could see a set of doubles having O2 in once cylinder and 100% He in the other is if someone filled them that way on purpose. There are too many steps involved for the doubles to wind up in this state for this to have been inadvertent.

Easy, start with a set of empty tanks and a PSI "recipe" for a particular TriMix blend, lets say 18/45

For the purpose of this example we will assume the calculated PSI numbers are all you need to use, no He or temp fudge factors.

Lets assume 3500 PSI tanks

you need 286 psi O2, 1575 psi He and 1640 PSI air.

Lets also assume you have 4 sets of dubs and 4 bottom stages and 8 deco bottles to fill also.

Normal practice would be to transfill / boost all the O2 first into all the tanks that need it. That means you are moving the din adapter and fill whip from tank to tank to tank, unless you have 16 din adapters. Doing the O2 first keeps the max O2 pressures down, and it means you aren't blowing the O2 out of the fill whips and booster after each tank, and don't have to keep swapping the inlet (inlet to the booster)whip back and forth between the O2 and He bank.

Then you repeat the process for He, i.e. fill all 8 of the tank /sets of dubs needing He in one setup.

Then top with air. Same deal, keep moving the din adapter from tank to tank to tank.


Let's say on one set of dubs you 1) have an un noticed Closed Iso, and you used the left post for O2 and the right post for He. Remember you are probably in a hot, cramped, crowded fill station and may be struggling to get the fill whips to reach all the tanks.

Then the phone rings just when you were going to do the air top on the dubs with the closed Iso.

Bingo you have set with 286 psi of 100% in one side and 1575 PSI of He in the other.

This requires a series of screwups, and a failure to analyze, but it's easily possible.

More likely would be 100% on one side and ~ 10/45 on the other (or the reverse) if the Air top was introduced to bring the tanks up to 3500 psi. In this case all that was required was a single filling error, leaving the ISO closed.
Worse if the diver skips analyzing and just looks at his SPG he may see a "full" set of dubs, and passes out on the surface.


Murphy never sleeps....


Tobin

 

[AfterDark]

Personally, I analyze on tank valve (or orifice or whatever the thing is called that you put the first stage on) if the regs are not installed. This is always the case when I pick up my tanks from the dive shop.

I analyze on a low pressure inflator hose if possible (backgas tanks) when I have regs installed.

In any case, I assume that the reading at the tank valve will be the same as the analysis on the second stage.




I wonder if anyone has any *actual* data or *real life* experience with this. The only way I could see a set of doubles having O2 in once cylinder and 100% He in the other is if someone filled them that way on purpose. There are too many steps involved for the doubles to wind up in this state for this to have been inadvertent.

Yeah me too, doesn’t everyone. You see I was posting under the mistaken impression we were discussing a hypothetical scenario where 2 manifold tanks. 1 with 100% O2 the other with 100% helium, and how mixing if any between those two tanks would take place. My theory was that any mixing would take place within the regulator the 1^st stage to be precise, and that analyzing what came out of the 2^nd stage would indicate what the mix if any was.It wasn’t a real world scenario it was made up.
Another posted that he had 2 manifold tanks with different gases in them and after a period of time he checked and there was no mixing between the tanks.I asked experimentally if the poster put a reg on one post and analyzed what was coming out of the 2^nd stage.

 

[Patoux01]

And just explaining why it doesn't matter that "it mixes in the regs" (which it most likely wouldn't, because what comes out the post is what goes in the reg), if you then have to close your manifold, you'll be on either pure O2 or pure He (assuming one tank is O2 and the other is He). Both would most likely make for an ugly result.

It's been written already, but it seems some didn't get it.

 

[AfterDark]

And just explaining why it doesn't matter that "it mixes in the regs" (which it most likely wouldn't, because what comes out the post is what goes in the reg), if you then have to close your manifold, you'll be on either pure O2 or pure He (assuming one tank is O2 and the other is He). Both would most likely make for an ugly result.

It's been written already, but it seems some didn't get it.

If the isolator is open then that reg is getting gas from both tanks. That’s how the manifolds work either reg can access all the gas in both tanks with one post closed. Now where else but the reg would those gases mix?

As I stated this was all theoretical on my part as I thought the discussion was; in the real world it doesn’t matter if any mixing takes places because I wouldn't dive with such a fill.

 

[Patoux01]

Either you have reading issues, or you are trying real hard not to understand.

Let's assume it would mix in the regs.

For some reason, eg the o-rings at one side of the manifold burst, you have to close the manifold.
So now it's closed again, no mixing anymore since you only have 1 tank left.
1) What are you breathing now? O2? He? If you remember that, it brings us to question 2.
2) How long do you have to live? On He, maybe a minute? On O2, it'll depend on the depth and how long you've been underwater already, but typically "not much".

Hope this is clear now.

 

[AfterDark]

Either you have reading issues, or you are trying real hard not to understand.

Let's assume it would mix in the regs.

For some reason, eg the o-rings at one side of the manifold burst, you have to close the manifold.
So now it's closed again, no mixing anymore since you only have 1 tank left.
1) What are you breathing now? O2? He? If you remember that, it brings us to question 2.
2) How long do you have to live? On He, maybe a minute? On O2, it'll depend on the depth and how long you've been underwater already, but typically "not much".

Hope this is clear now.

It was never unclear to me anyway.

---------- Post added June 24th, 2015 at 10:54 PM ----------

Which is why I posted the above. Seems to me you may have reading issues sir.

 

[nimoh]

'
I didn't post the mixing takes place in the 2nd stage, I posted it takes place within the regulator. I thought I was posting in the Advanced site so I didn't think anyone would make the assumption that I was referring to mixing in the 2nd stage, but it would be easier to check what comes out of the second stage than what is in the 1st stage don't you think?

I thought we were discussing 2 tanks one with 100% O2 and 1 with 100% helium minimal mixing would happen in the manifold but the 1st stage would be receiving two kinds of gases and some mixing would happen within the 1st stage.. I was thinking it would be experimental to check what the %'s of each gas coming out of the 2nd stage would be, not some kind of halfassed attempt to fix to a bad fill.

I get a bad nitrox fill, it's a do over or I don't pay.

sorry, guess I misunderstood. However, it's actually easier to test what comes out of the first stage, just plug your analyzer into the lp inflator hose.

 

[Doppler]

If the isolator is open then that reg is getting gas from both tanks...

My understanding is that when one breathes from a regulator on a set of doubles with the isolator open, the gas delivered is drawn initially and primarily from the tank to which the reg is attached. There is a slight lapse (perhaps a second or two) between inhalation and the pressure being equalized as gas transits across the manifold to re-establish equilibrium. I do not believe there is any "mixing in the first stage."

Certainly would be interested to read the results of any experiment!